Innate immunity – barriers, inflammation and phagocytes
BiologyHealth & DiseaseAges 16–17
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Sign in to playA tissue model at a wound: mast cells release histamine, blood vessels widen and become leaky, neutrophils and then macrophages arrive by chemotaxis and engulf bacteria, complement marks the bacteria, a clot seals the wound and fever appears in severe infection. Vary the number of bacteria, the wound and the body's condition and follow bacteria, redness and swelling hour by hour. Extra screens show the steps of phagocytosis, the barriers (skin, mucus and cilia, stomach acid, tears) and a comparison of innate and adaptive immunity.
Lesson: Innate (non-specific) immunity: barriers, inflammation and phagocytosis
What it shows
This model shows the body's first, non-specific defences. Skin, mucus with cilia, stomach acid and tears with lysozyme stop most microbes. When bacteria enter a wound, a clot seals it and mast cells release histamine: arterioles widen (redness, heat) and capillaries leak plasma (swelling). Neutrophils, then macrophages, follow chemical signals and engulf the bacteria; complement marking speeds this up. If bacteria multiply faster than they are engulfed, the infection spreads and fever appears. Counts, rates and barrier probabilities are simplified model values, not clinical data.
How to use
On Inflammation, set Bacteria, Wound and Condition, then press Run; drag across the graph to look back, and compare runs in the table. On Phagocytosis, pick a Phagocyte and step with Back and Next. On Barriers, choose an Entry route and a Barrier state and press Release 20 bacteria. Compare shows innate and adaptive immunity side by side. Tap a picture to hide labels.
Parameters you can change
- Screen Inflammation at a wound, Steps of phagocytosis, Barriers to entry, Comparison with adaptive immunity
- Bacteria entering the wound 100–10000 bacteria
- Wound Unbroken skin (no wound), Shallow scratch, Deep cut
- Body condition Normal, Taking an antihistamine, Low neutrophil count, Complement deficiency
- Phagocyte Neutrophil, Macrophage
- Entry route Skin, Airways, Stomach, Eye
- Barrier Working normally, Damaged
Questions to explore
- Why does an inflamed wound become red, warm, swollen and painful?
- An antihistamine reduces swelling, so why do the bacteria survive a little longer?
- Why can a small wound lead to a serious infection in someone with a low neutrophil count?
